The present invention relates to a system and method for automatically controlling a vehicle speed to a desired cruising speed.
A kind of system for automatically controlling vehicle speed to the desired cruising speed is exemplified by a Japanese Patent Application First publication (Tokkai) No. Sho 60-163735 published on Aug. 26, 1985.
In the above-identified Japanese Patent Application document, the automatic vehicle speed controlling system includes a command switch group used for controlling the vehicle speed to the desired cruising speed and a vehicle speed sensor. The command switch group includes a set switch for operatively commanding the cruising speed control, an acceleration switch, and a resume switch (reset switch). In addition, the automatic vehicle speed controlling system includes an actuator for actuating a throttle valve in the vehicle's engine to open or close at an angular position thereof in response to an input signal. The actuator includes a vent valve, a safety valve, and a vacuum valve. When the vacuum valve is opened and simultaneously the vent valve is closed, a negative pressure is introduced into a pressure chamber of the vacuum valve so that the throttle valve is actuated to displace toward an open direction. When the vent valve is opened and simultaneously the vacuum valve is opened, atmospheric pressure is introduced into the pressure chamber so that the throttle valve is actuated to displace toward a close direction.
Furthermore, a brake switch and a clutch switch are also installed to detect a depression of the brake pedal and to detect a depression of the clutch pedal, respectively.
When the vehicle driver depresses the brake pedal or depresses the clutch pedal during automatic cruising speed control by the automatic vehicle speed controlling system, the adjustment of the throttle valve by means of the actuator is released. At this time, the vehicle speed deviates from a set vehicle speed in response to the off operation of the set switch and the set vehicle speed is stored in a storage unit of the automatic vehicle speed controlling system. In this state, when the reset switch is once closed (ON) and again opened (OFF), the vehicle speed is returned to the set vehicle speed without operation of the set switch.
When a vehicle speed difference between the set vehicle speed and the actual vehicle speed exceeds a predetermined value during the return of the vehicle speed to the set vehicle speed, a constant acceleration control for the vehicle is carried out such that the opening angle of the throttle valve is adjusted so that the rate of increase in the vehicle speed coincides with a predetermined rate. When the vehicle speed difference becomes reduced and below the predetermined value, the automatic cruising speed control system enters the cruising speed control.
In the conventional vehicle speed controlling system disclosed in the above-identified Japanese Patent Application document, since a transfer point at which the vehicle speed control is transferred from the constant acceleration control to the automatic cruising speed control is set when the difference between the actual vehicle speed and the set vehicle speed drops below the predetermined value, the predetermined value needs to be adjusted according to models of vehicles on which the automatic vehicle speed controlling systems is mounted. This is because engine output characteristics and so on are vary according to the model of the vehicle. If the predetermined value is not changed according to the model of the vehicle, an overshooting of the vehicle speed occurs and a long time occurs before the vehicle speed settles at the set vehicle speed. Therefore, since the transfer point needs to be adjusted for each of the models of vehicles on which the above-described system is mounted, so that the adjustment operation becomes troublesome and costly.